The present invention relates to an improved tibial prosthesis, template and reamer. The bearing surfaces of the knee joint are vulnerable to stress and arthritic and other disease-induced deterioration. Prosthetic correction is indicated when the knee joint is so damaged that other less drastic techniques have little or no prospect of success. In earlier years, hinge-type prostheses were most frequently employed in such cases to restore the joint to some degree of normalcy. This was not entirely satisfactory due to the complexity of the knee joint movement, the desirability of minimal bone removal, the need for preserving potentially functional cruciate and collateral ligaments, and the limitations of hinge-type prostheses in handling various knee loads and forces without being damaged. Hinge-type prostheses are generally limited today to cases with severe soft tissue damage. Later and present knee prostheses have separate femoral and tibial components attached to the respective femoral and tibial condyles so as to provide a prosthesis more in harmony with the actual workings of the knee joint. Separate components allow use of the existing cruciate and collateral ligaments and permit the prosthesis to handle radial and twisting forces on the knee without breaking.
Although the prior art as embodied in separate tibial and femoral components has become more sophisticated as of late, to this time, tibial prosthetic components do not ideally replace the bone tissue since their shapes and means of attachment do not optimize the uniform spreading of forces which are placed on the tibia nor do they adequately oppose lateral motions which are inherently placed upon tibial components during normal joint movements. Thus, in the prior art, tibial components often loosen and must be reattached or replaced with such operations often requiring removal of additional bone tissues.
In a further aspect, many tibial components known at this time are attached to the proximal tibia through the use of cementing techniques. This may cause problems in the joint since these cementing techniques usually result in elevated temperatures during the curing of the cement, which elevated temperatures tend to damage body tissues. Thus, a need has developed for a tibial prosthesis which may be installed without the use of cement but which may consistently achieve firm initial fixation and thence may receive bony ingrowth for firm permanent fixation.
The tibial component of a knee prosthesis is generally cemented to the tibial condyle rather than screwed thereto because a satisfactory environment for uncemented devices has not been taught by prior art. Earlier tibial components such as that which is disclosed in U.S. Pat. No. 3,728,742 to Averill had serrations and pins on the underside which were anchored in the proximal tibial surface by a suitable cement after surgical preparation. The problems with cemented prosthesis have been discussed hereinabove and components such as those disclosed by Averill have been known to be vulnerable to loosening from typical knee forces which are placed on the prosthesis.
In order to avoid the problems of Averill, the configuration of the tibial component further evolved to a point where a vertical element extending downwardly from the undersurface of the tibial component and into the tibia has been used to counteract instability problems. U.S. Pat. No. 4,205,400 to Shen, et al. discloses a tibial prosthesis having a base plate formed with a depending connecting stem which is designed to extend distally into the proximal tibial surface into a cavity excavated therein by the surgeon. This device is believed to be deficient in that it requires a large amount of bone removal and still requires the use of cement which has the problems as set forth hereinabove.
Additionally, the following prior art is known to applicants:
U.S. Pat. No. Re. 29,757 to Helfet discloses prosthetic joint components including double curved surfaces as well as an elongated post for fixation purposes. The teachings of Helfet differ from the teachings of the present invention mainly because the present invention does not require an elongated fixation spike and further because the present invention utilizes fixation means which may comprise screws extending through the curved surfaces thereof.
U.S. Pat. Nos. 4,224,696 and 4,224,697 both to Murray, et al., disclose a prosthetic knee having femoral and tibia components both of which are made of a biologically inert high strength metal such as chromium-cobalt-molybdenum. The meniscal plate is a one-piece unit of ultra-high molecular weight polyethylene and fixed between the femoral and tibial components. The underside of the tibial component include a substantially curved surface but also requires an elongated anchoring spike. Of course, this anchoring spike renders the tibial prosthesis of Murray, et al. vastly different from the teachings of the present invention and Murray, et al. also fail to disclose the type of fixation utilized in the present invention.